Improving Safety Through Arc Flash Technology

Copyright © 2011 Rockwell Automation, Inc. All rights reserved.

Educational Session A: Improving Safety Through Arc Flash TechnologyJohn A. Kay, CETSenior Product Specialist,Medium Voltage Technologies

V11.7.1

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Agenda


1. Arc Dynamics

2. What is arc resistance equipment all about?

3. Global arc resistant testing guides and standards

4. How these guides and standards affect what you specify

5. What are the key aspects to arc resistant product specs

6. How are arc resistant equipment designs tested

7. The role arc resistant products play in your safety program

8. Compliance to current NFPA-70E requirements

9. What’s on the horizon?

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NFPA 70E Defines an Arc Flash Hazard as….

“..a dangerous condition associated with the release of energy caused by an electric arc.”

Flash FactsSurface of the sun- 9,032F

Arc Flash core- 35,000FSource- NASA, NOISH


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Faults Exhibited in Electrical Circuits

Bolted Fault – current flowing through bolted bus bars or other electrical conductors.

• A bolted fault test is standard for all MCCs, Switchgear and most electrical designs

• It is an electro-mechanical test, i.e. bus/cable bracing

Arcing Fault – current flowing through air • Always lower current than bolted fault current• Voltage drop across the arc due to resistance within the arc

plasma


Specify bolted fault & arcing fault currents levels separately!THEY ARE NOT THE SAME! IBF is always more than IAF

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Arc Flash/Blast Dynamics

35,000° F

Intense LightCopper Vapors (Expansion rate

67,000 times)

Shrapnel Molten Metals

Sound & Pressure

Waves

Intense Heat Expelled


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Characteristics of an Arc Flash

• A conductive plasma, which has a much lower impedance and much higher conductivity than air

• The flash occurs virtually instantaneously, releasing a huge amount of energy in a very short period of time

• A large pressure wave is created by the expansion of the super heated air and the vaporized materials

• Melts and vaporizes components - flooding the air with more conductive particles

• The available short circuit current has a major influences on the energy released in the arc* *-other factors also must be considered!


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Dynamics Stages of Arc in an Enclosure

• Compression

• Expansion

• Emission

• Thermal

Pressure

Current

Arc Voltage

1 2 3 4

1

2

3

4


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Typical Arc Pressure & Temperature Profile

2·105 Pa(~29 PSI)

>12,700 C(>23,000 F)

Pressure [Pa]

Temperature [C]

10 20 30 100 200 ms

t

T & P

Cable fire (~600°C)

Copper fire (~1100°C)

Steel fire (~1550°C)

I²t, kA² scalories

Opening time of a 5 cycle breaker (83 ms) NOT

including relaying latency

Total clearing timewith coordinated

overcurrent protection

(up to 225 ms ) typical

Extensive damage to equipment and critical

injury to personnel >250 ms


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How Long Can Arcing Occur?

• The arc will continue as long as,– The voltage available is high

enough to sustain it– Current continues to flowing in

the arc plasma– There is fuel to ‘feed’ the arc

– materials that can provide the ions necessary to sustain current flow within an air mixture


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Arc Resistant Equipment

• Arc Resistant is a term used to describe how a piece of equipment resists the effects of an internal arc fault (relates to arc flash exposure)

• The level of arc flash protection is defined by the level to which an arc flash/blast is:– Extinguished or Controlled– Channeled away from personnel– Prevented from propagating

• Testing must be performed to validate a level of resistance (protection)– Defined as the “Arc Resistant Accessibility Rating”

• The equipment manufacturer is responsible to test to a given standard or guide to validate a given accessibility rating.


The Accessibility Rating defines one of the performance characteristics for arc resistant equipment….

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• EEMAC G14-1-1987 “Procedure for Testing the Resistance of Metal-Clad Switchgear under Conditions of Arcing Due to an Internal Fault”

• IEC 62271-200 “AC Metal-Enclosed Switchgear and Controlgear for Rated Voltages Above 1 kV and up to and Including 52 kV”, Annex A - Internal Fault

• IEC 61641-2008 “Enclosed low-voltage switchgear and controlgear assemblies – Guide for testing under conditions of arcing due to internal fault”

• IEEE C37.20.7-2007 "IEEE Guide for Testing Metal-Enclosed Switchgear Rated Up to 38 kV for Internal Arcing Faults”

• CSA C22.2 NO. 0.22-11 “Evaluation Methods for Arc Resistance Ratings of Enclosed Electrical Equipment”

NEW!

Common Arc Testing Guides & Standards


Many global guides and standards for AR equipment …..Compliance to one does not mean compliance to the others!

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Global Accessibility Types

Type A-Front onlyEEMAC Type B-Front, back, sides

Type C-Front, back, sides, & compartmental

Type 1-Front onlyIEEE, Type 2-Front, back, sides

CSA Suffix A-Used if no other suffix appliesSuffix B-Control compartment* (new in 2007)

Suffix C†-Adjacent Compartments protection

Type A-Accessible to authorized PersonnelIEC Type B-Accessible to general public

Type C-Pole top equipment


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IEEE Accessibility Type 1

Illustrative graphic only. Additional PPE may be required.Copyright © 2011 Rockwell Automation, Inc. All rights reserved.

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IEEE Accessibility Type 2

Illustrative graphic only. Additional PPE may be requiredCopyright © 2011 Rockwell Automation, Inc. All rights reserved.

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IEEE Accessibility Type 2B

LV Control Compartment

Illustrative graphic only. Additional PPE may be required.Copyright © 2011 Rockwell Automation, Inc. All rights reserved.

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Other Arc Resistant Specifications

• Arc Fault Current Level– The tested level of arcing current

• Varies by equipment type, system voltage, manufacturer and global region• Typical values are 10kA, 25kA, 31.5kA, 40kA, 50kA, 60kA• Testing guides permit any level

• Arc Duration– The time the arc was sustained for the test

• Nominal is 0.10, 0.25, 0.5, 1 or 3 second ratings • Typically 0.5 seconds is used (suggested max. by IEEE)• Varies by vendor• Testing guides permit any time period


Testing guides permit any levels

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Other Arc Resistant Specifications, con’t

• Mechanical Considerations– Top & Bottom exit/entry- don’t assume both are available

• Not all arc resistant controller suppliers can provide top exit!– Footprint could be bigger than non-arc resistant designs

• Important for room layouts– You’ll need more ceiling height– Gas plenums or chimneys?

• Where are they located?


There are more things to take into account when installing arc resistant equipment!

Plenum & Chimney Installation Considerations

• Where should the energy from an arc flash be directed?– Within the building assumes an area can be made

inaccessible to personnel and no flammable materials are present

– Externally is generally preferred, implying that a barrier be used to restrict the entry of weather or vermin

• If the arc gases are going to be released into a small control room or building that houses the arc resistant equipment, it must be designed to withstand:– Overpressure, up to 15-20 psi, on a transient basis– The effects of hot gases and flames as they are released into the room (i.e.

non-flammable construction materials are required)– Special ventilation may be required

19Copyright © 2011 Rockwell Automation, Inc. All rights reserved.

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Other Aspects to Consider

• NEMA based Testing Guides don’t fully cover LV MCCs!– IEEE C37.20.7-2007 now includes consideration for metal-enclosed Low Voltage

power circuit breaker switchgear– Standard is under review and revision currently– Difficult to find a consensus due to various manufacturers designs

• Rockwell Automation has always used IEEE C37.20.7 as a guide for testing both their LV & MV MCC– IEC products are tested to the appropriate IEC guide

• Bulletin 2500 IEC LV MCC tested to IEC 61641-2008• Bulletin 7700 IEC MV MCC tested to IEC 62271-200

Flash FactsOSHA Lockout/Tagout standard, which outlines the

MINIMUM requirements to control hazardous energy, was the 5th most frequent cited violation from fiscal

year 2005 to 2009Source- OHSA


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How Are The Tests Completed?


LV MCC Prototype tests!

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Test Setups Vary by Global Testing Guides

Generally• Flammable cotton indicators are placed vertically around the test unit as

follows:– Vertical indicators are placed 100 mm from the enclosure walls

• From the floor to a height of 2 m (79”)• Facing areas thought to be likely to emit gases

• Indicators cover the area being evaluated, seams etc.• Horizontal indicators are placed at a height of 2 m (79”) above the

mounting surface and parallel to the floor– Indicators extend beyond the switchgear by at – least 300mm, 1000 mm typical

• Each testing guide has slight changes to the electrical configurations


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Typical Test Setup


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Horizontal Indicators


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MV Unit Under Test


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A Successful MV Arc Test


Passing an Arc Test Generally Means:

• Doors and covers do not open (bowing allowed)

• No parts are ejected from the equipment• The arc does not burn any holes in the exterior

of the tested structure (in the applicable planes for the accessibility level)

• 150 mm2 (6 in2 ) – 150 g/m2 Cotton test indicators at a distance of 100 mm (4 in) must not ignited or be perforated, (approximates typical industrial work clothes)

• The grounding connections remain effective

27Copyright © 2011 Rockwell Automation, Inc. All rights reserved.

Performance criteria varies by testing guide

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Arc Resistant Equipment Considerations

• Arc resistant equipment should been tested to a relevant testing guide or standard

• Certification Letter or Letter of Attestation should be available to corroborate the claimed results

• Not included in the existing Nationally recognized testing standards for LV and MV motor controls– UL 845 – “Standard for Motor Control Centers” does

not address arc fault performance• Specific performance criteria is mandated under bolted

fault, short circuit conditions for electric shock and fire hazards

– UL 347, for MV MCCs, also does not include content related to arcing faults


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Keeping it “Arc-Resistant” When I Use it

This requires that, • The equipment is properly installed in accordance with only the

manufacturer’s instructions• All* doors and covers be properly secured (*- for type 1B or 2B the LV controls

compartment door can be open)– If any door or cover is open to a medium voltage compartment, the equipment is

not in its “arc-resistant” condition and the level of protection to personnel will be compromised!

• Any exhaust vents must be free of obstructions• Extra care in cable installation


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Where are These Standards Taking Us?

Enhanced Safety

Arc resistant Switchgear-1990’sNFPA-70E-2000

IEEE 1584-2001NFPA-70E-2003

CSA Z-462-2008NFPA-70E-2009

NFPA-70E-2012CSA Z-462-2012


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So Now What?

NFPA-70E is your guide…• To understand your risk areas, you need to perform and maintain an arc

flash hazard study within your facility, – If you don’t, you must adhere to the data and guidelines provided within NFPA-70E

regarding PPE, boundaries, etc.• Label electrical equipment, based on the study, to indicate,

– The level of the arc flash hazard (incident energy)– The PPE requirements– The boundaries defined by NFPA-70E

• Obtain and maintain the appropriate Personal Protective Equipment (PPE)


Rockwell Automation can perform complete arc flash hazard studies and provide risk mitigation solutions

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So Now What?

• You need to determine the extent of the risk- you may not require AR equipment!– Your arc flash study will give you the facts!!!

• It is the electrical system designer, constructor, and user/owner who are responsible to define, manage and mitigate risks to a tolerable level

• Develop, implement and train proper work place safety policies, procedures and methods

• Train the workers (both internal and contract) • You must actively update and audit the safety program in your facility


Rockwell Automation can assist you with these tasks!

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So What is OHSAs Position on All of This

• “…Industry consensus standards can be evidence that there is a hazard for which that PPE is "necessary." While the NFPA 70E consensus standard has not been adopted as an OSHA standard, it is relevant as evidence that arc flash is a recognized hazard and that PPE is necessary to protect against that hazard….”

• “…An flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use…”


Failure to protect workers will result in OHSA prosecuting to the fullest extent of the law, based on these premises

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So What is OHSA’s Position on All of This

• Complacency is a major danger to anyone working around electrical energy

• Appropriate PPE should ALWAYS be used• Not only should OHSA and like standards be followed, but all employers

must adhere to the consensus standards- like NFPA-70E

Flash FactsElectrical hazards are one of the top causes of workplace deaths and violations of electrical standards routinely top OSHA’s list of cited

violations.Source- OHSA


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How can AR Equipment Help?

• Can be a part of the overall protection strategy• MV arc resistant equipment can reduces the hazard/risk category to

Level 0– The lowest level defined by NFPA-70E!– For LV MCCs see Article 130.7/(C)(15)(a)- no reduction at this point

• May simplify your safety program• Select an accessibility type that best suits you requirements – e.g. Type

2B• Always refer to NFPA-70E for details!


Arc resistant equipment reduces the hazard/risk category to Level 0- the lowest level defined by NFPA-70E

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How Can Rockwell Automation Help?

7.2kV NEMA & IEC MCCs

LV NEMA MCC15kV IEC MCCs LV IEC MCC


ArcShield & ONEGear Arc resistant LV and MV MCCs

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FEW STANDARDS

TO SUPPORT

What Else is on the Horizon

• Light/current based arc detection systems- available now!• Personal arc detection sensors- available now!• Arc clamping devices- available now!• Pre-emptive arc detection technologies

– In develop stages– Predicts immanent failures– Still doesn’t address the human factor….but..

• Human-Machine Interaction Bioengineering• Safety in Design• Understanding, more thoroughly, the interaction of humans


Future Technologies For the Future

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Other Ways We Can Help……

• On Site Training including Arc Flash Training• On site data collection, Arc Flash Analysis, Protective Device

Coordination Studies, Short Circuit Analysis and Arc Flash Labeling• Category Mitigation Services (Design and Engineering)• Written Program Services• Electrical Work Permit Services• Ongoing support for the updating of site electrical diagrams and the

labeling of new panels• Reporting using industry recognized software tools


Rockwell Automation is your partner in machine safety!

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Key Points and Take Aways!!!!

• You must have a up to date and maintained safety program• You should have a maintained arc flash study of your facilities• You must have your equipment properly labeled• You must have the necessary PPE available based on your study• Arc resistant equipment can be a critical part of your overall safety

program• Arc resistant equipment can vary dramatically between vendors• Certification guides and standards continue to evolve• Guides and standards are behind the technological improvements


Rockwell Automation is your partner in creating a comprehensive safety program compliant to NFPA-70E!


Questions

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Improving Safety Through Arc Flash Technology